Both motors and generators have been known to use axial-based rotor and stator configurations, which can experience several phenomena during operation. For example, conventional axial motor and generator structures can experience detent, which is also known as “cogging torque” or “detent torque.” Detent can be described as a periodic torque that can arise in motors and generators that co-axially integrate magnetically permeable elements, such as field poles, to form a stator structure, and use permanent magnets to form a rotor structure. When either the stator or rotor structure is rotated with respect to the other, a periodic varying torque can be created because the magnet structure typically prefers to align at a position that is centered with the magnetically permeable elements rather than at the intervening field pole gaps of air between the field pole elements.
FIG. 1A illustrates a traditional electric motor exemplifying commonly-used stator and rotor structures. Electric motor 100 is a cylindrical motor composed of a stator structure 104, a magnetic hub 106 and a shaft 102. The rotor structure of motor 100 includes one or more permanent magnets 110, all of which are attached via magnetic hub 106 to shaft 102 for rotation within stator structure 104. Stator structure 104 typically includes field poles 118, each having a coil winding 112 (only one is shown) that is wound about each field pole 118. Stator structure 104 includes slots 108 used in part to provide a wire passage for winding coil wire about stator field poles 118 during manufacturing. Slots 108 also provide magnetic separation between adjacent field poles 118. Stator structure 104 includes a peripheral flux-carrying segment 119 as part of magnetic return path 116. In many cases, stator structure 104 is composed of laminations 114, which typically are formed from isotropic (e.g., non-grain oriented), magnetically permeable material. Magnetic return path 116, which is one of a number of magnetic return paths in which permanent magnet-generated flux and AT-generated flux is present, is shown as being somewhat arcuate in nature at peripheral flux-carrying segment 119 but includes relatively sharp turns into the field pole regions 118.
Another drawback of conventional electric motors is that laminations 114 do not effectively use anisotropic materials to optimize the flux density and reduce hysteresis losses in flux-carrying poles, such as through field poles 118, and stator regions at peripheral flux-carrying segment 119. In particular, peripheral flux-carrying segment 119 includes a non-straight flux path, which limits the use of such anisotropic materials to reduce the hysteresis losses (or “iron losses”). Hysteresis is the tendency of a magnetic material to retain its magnetization. “Hysteresis loss” is the energy required to magnetize and demagnetize the magnetic material constituting the stator regions, wherein hysteresis losses increase as the amount of magnetic material increases. As magnetic return path 116 has one or more turns of ninety-degrees or greater, the use of anisotropic materials, such as grain-oriented materials, cannot effectively reduce hysteresis losses because the magnetic return path 116 in peripheral flux-carrying segment 119 would cut across the directional orientation of laminations 114, such as direction 120, which represents the orientation of grains for laminations 114.
While traditional motor and generator structures are functional, they have several drawbacks in their implementation. It would be desirable to provide improved techniques and structures that minimize one or more of the drawbacks associated with traditional motors and generators, including axial motors.